Coupled cavity resonator



Aug. 24, 1948.

V. L. RONCl COUPLED CAVITY RESONATOR Fi led Jan. 10, 1944 FIG. 2

2 Sheets-Sheet 1 INVENTOR' y 1 L. RONC/ A TTORNEY Aug. 24, 1948. v. L.RONCl 2,447,537

COUPLED CAVITY nmsomuron F il'ed Jan. 10, 1944 2 Sheets-Sheet 2 I v.INVENTOR 55% V By ML. RONC/ A TTORNEV Patented Aug. 24, 1948 UNITEDSTATES ATENT OFFICE COUPLED CAVITY RESONATOR Application January 10,1944, Serial No. 517,660

9 Claims.

This invention relates to coupled systems of cavity resonators,particularly for use in multianode magnetrons, in which interanodestraps are employed to influence the separation of the resonantfrequencies and in which the straps are shielded to reduce theirreaction with the electromagnetic field in the space between the cathodeand the anode segments.

The resonating systems commonly employed in multianode magnetronscomprise a plurality of resonating cavities which are coupled, theresonating system as a whole, on account of the coupling, necessarilyhaving a plurality of resonant frequencies at least as numerous as theanode segments. The distribution and separation of the resonantfrequencies are dependent upon the nature and degree of the couplingbetween the cavities, often in a very complicated manner. Upon operationof a given resonant structure in an oscillator, the oscillations areusually found to be restricted to one of the several resonantfrequencies, the particular one depending upon various parameters of theexcitation system. Some times during operation the operating frequencymay change in an erratic and unpredictable manner from one resonantfrequency to another. For each resonant frequency the distribution ofcurrents and electric and magnetic fields has a characteristic patternand theoperation of the system with a particular pattern is termed amode of oscillation. Usually the modes of oscillation are distinguishedfrom each other by different frequencies, although in special cases twomodes may have the same frequency but a different pattern of currentsand fields.

In practice it is usually desirable to design a magnetron for aparticular mode of oscillation and to discourage orprevent oscillationat other modes. It has been found that the particular mode ofoscillation which will be set up in a given system may be influenced bythe use of conductive straps connecting predetermined selected points ofthe anode structure. The straps, among other possible effects, introducemore or less concentrated capacitances between surfaces of straps whichare opposed and between surfaces of the straps and adjacent portions ofthe anode. These capacitances have been found to influence theseparation of the resonant frequencies. It has also been found that thetendency of the magnetron to confine its oscillations to a particularmode increases with the degree of separation.

It was early noted that in many instances the efliciency of powerconversion in strapped magnetrons was markedly less than in otherwisesimilar magnetrons without straps. A notable exception was found inmagnetrons having a particular form of strapping, known as echelon, inwhich the straps were so arranged that the high potential portion of agiven strap was shielded from the cathode-anode space by a low potentialportion of another strap situated between the first-mentioned strap andthe cathode-anode space. Experiments which have been performed toexplain the greater efficiency of the magnetron with echelon strappingindicate that unshielded straps tend to distort or disturb theuniformity of the pattern of the electric and magnetic fields near theends of the anode structure. It may be assumed that an unstrappedmagnetron that is highly efiicient has a pattern of fields in the spacebetween the cathode and anode particularly favorable to efiicient energyreaction with the electrons in that space. If the same magnetron, whenequipped with straps is found to be less efiicient than before, thedifference is evidently due, at least in part, to disturbance of thefield patterns near the ends of the anode structure whereby thefavorable field pattern no longer extends over as large a portion of thelength of the anode. To restore the former efficiency, shielding may beinterposed between the straps and the cathode-anode space.

The purpose of the present invention is to provide a highly efiicientarrangement for shielding the high potential strap areas. In accordancewith the invention, the straps are mounted upon a ledge depressed in theend of the anode structure and shielding elements are provided in theform of tabs attached to the straps and bent so as to occupy positionsbetween the cathodeanode space and the high potential strap areas. Theresult is a structure and arrangement of the anode, straps, and shieldswhich'has been found to be effective in promoting efilciency in,magnetrons as well as in confining the oscillations to a desiredparticular mode. The structure is at the same time simple and economicalto manufacture.

While the strapping and shielding system is applicable to multicavityresonators in general, the arrangement is illustrated herein as embodiedin a magnetron.

In the drawings:

Fig. 1 is an 'elevational view of a magnetron embodying the invention,partly dismantled and partly in section;

Fig. 2 is an elevational view from one end of the anode showing the samestructure as in Fig. 1, partly broken away and partly in section;

Fig. 3 is an enlarged detail plan of the end of the anode opposite theend shown in Fig. 2;

Fig. 4 is a fragmentary perspective view of one end of the anode, brokenaway to show a ledge in the anode structure before the insertion ofstraps and shields;

Fig. 5 is a fragmentary view of a portion of the anode with straps andshields in place; and

Fig. 6 shows the superficial appearance of the assembled magnetron.

Referring to the drawings, [0 is an anode structure and resonatingsystem comprising a perforated cy lindrical block of conductive materialand H is a cathode of cylindrical form concentrically mounted in acentral reaction space in the anode block as shown in Fig. 1. Thecentral reaction space with the cathode removed is shown at l2 in Fig. 3and preferably comprises a cylindrical bore coaxial with the block l0. Aplurality of resonating cavities are formed in the block 10 as by boringa plurality of cylindrical holes 13 having their axes lying on animaginary cylinder coaxial with the block In, the holes l3 beingconnected with the reaction space by individual slots 14, preferablyradial.

. The anode block is preferably fashioned to provide end spaces l5 andH5 at either end. The block has a plane face I! intersecting thereaction space I2, the cavities l3 and the slots I4 substantially atright angles to the axis. At the opposite end of the block there is acorresponding plane face l8. The end spaces are preferably closed by endplates 19 and 20 which may be of suitable magnetic material such as ironor steel to facilitate the application of a strong magnetic field to thereaction space [2 by means of an external magnet or magnets inwell-known manner. The end face i! is shown in Fig. 4 in a view with theend plate i9 removed and with part of the outer shell cut away.

The arrangement of the straps and the shielding thereof is shown indetail in Fig. 5. A ledge is first cut in the end of the anode. This maybe done conveniently by boring a shallow axial hole concentric with thereaction space l2 and of sufficient diameter to include the slots l4 anda portion of the cavities l3. A portion of the periphery of such a holeappears at 2! in Fig. 2 and a portion of the periphery of a similar holeat the other end of the anode appears at 22 in Fig. 3. The hole isextended to the desired depth to accommodate the straps which are to beemployed. The bottom of the hole is preferably defined by a flat surfaceintersecting the material of the block between the respective slots M toform anode segment end faces such as 23, 24 and 25 in Fig. 4. Two of theanode segment end faces 24 and 25 are shown in greater detail on anenlarged scale in Fig. 5, with a fragmentary view of straps in place andmeans for shielding the straps in accordance with the invention. Planviews of the straps and shields at either end of the anode are shown inFigs. 2 and 3, respectively.

The straps comprise ribbons or rings 26 and 21 of conductive material.Attached to or preferably integral with the ring 26 are a plurality oftabs which are bent into a U-shape. The horizontal portion of the U issecured and electrically connected to one of the anode segment faces inany suitable manner. Such a horizontal portion 28 of a tab is shownattached to the face 24 in Fig. 5 by means of a small amount of solderor brazing material 58. The vertical portion 29 of the tab is preferablymounted .fiush with the cylindrical surface of the anode segment andserves to shield th reaction space l2 from the electromagnetic influenceof the straps 26 and 21. The ring 21 passes over the horizontal portion28 and behind the vertical portion 29 of the tab attached to the ring26. The ring 21 has a plurality of tabs also bent into a U-shape. Thehorizontal 3!) portion of a tab is attached and electrically connectedwith one of the anode segment faces such as 25. The same tab has avertical portion 31 which rises flush with the cylindrical face of thecorresponding anode segment. The ring 26 passes behind the ring 21 inthe neighborhood of the tab 3!), 3|.

In the embodiment illustrated in Fig. 2, the ring 28 is attached toalternate anode segments and the ring 21 is attached to the segmentsintermediate to those to which the ring 26 is attached. As shown in 2,the rings may be split to facilitate assembly or to conform with anydesired scheme of interconnection of the anode segments. In Fig. 2 theends of the straps are shown as separated by slight gaps 59 and 60whereas in Fig. 3 the ends are shown as joining together at the centerof a split tab as at BI and 62. As illustrated by Figs. 2 and 3, thearrangement and connection of the straps may be different at the twoends of the anode.

The cathode l I pref erablyhas a coating of thermionically highlyemissive material and encloses a heating winding. The cathode assemblymay be supported by a pair of heater leads 32 and 33. Each heater leadis in turn supported by a tubular glass seal 34 and a bushing 35. Thebushing has a tapered flaring edge 36 to the inner surface of which theglass may readily be sealed.

An output coupling arrangement is provided by means of an inductive loop'31 inserted into one of the resonant cavities through a radial bore 38.The two ends of the loop 31 are connected respectively to the inner andouter conductors of a coaxial output fitting. The outer conductor of thecoaxial fitting comprises a cup-shaped member 39 sealed into the hole 38and supporting a cylindrical conductive sleeve 40. The cup 39 and oneend of the loop 31 are mechanically and electrically connected to theanode ill in any suitable manner such as oven brazing or soldering. Theinner conductor of the coaxial fitting comprises a succession ofcylindrical conductive members H, 42 and 43, of which the member 4! hasa tapered end which is centrally bored to receive one end of the loop 31as shown in Fig. 2. The member 43 contains a socket to receive the innerconductor of a coaxial transmission line (not shown). The outerconductor of the transmission line is preferably arranged to slide overthe member 48 when the inner conductor is inserted into the socket ofthe element 43. A glass seal 41 is suitably arranged between the insideof the sleeve 40 and the outside of the member 43 as shown in Fig. 2.

The coaxial output fitting may be protected by a sheath 44 (Fig. 6)having a slot 45 to receive a pin projecting from the coaxial line andthe open end of the sheath may be threaded as shown at 63 to receive aretaining ring. The sheath 44 may be attached by means of screws 64 tothe flange 46 (Fig. 2) of the cup 39.

For convenience in pumping out the structure to the desired degree ofvacuum, a small hole 43 (Fig. 1) is drilled into the anode and a bushing49, similar to the bushings 35, is fitted around the hole 48. Thebushing 49 preferably includes a flared and tapered portion 50 to whichmay be sealed a glass tube for use in pumping. The glass tube may besealed off after evacuation in the usual'manner to form a tip 5| asshown in Fig. 1.

The bushings 35 and Mlmay be externally threaded to receive protectingsleeves 52, E53 and 54, of which 52 and 53 terminate in conductivecontact tips 55 and 563 for electrical connections and the sleeve M isclosed off at the bottom to protect the glass tip 5!. A plurality ofcooling fins 51 (Fig. 6) are preferably arranged on the exterior of theanod block l0.

I he magnetron disclosed is adaptable to being built on any suitablescale of magnitude according to the frequency at which it is desired tooperate. In an embodiment that has been built for operation in theneighborhood of 3,000 megacycles centimeters wavelength) the cylindricalborings I3 have a diameter of 0.356 inch and are placed with theircenters on a circle of 1.17 inches diameter. The reaction space I2 is of0.567 inch diameter and the slots M are 0.072 inch wide. The diameter ofthe ledge at the periphecry 2! or 22 is 1.058 inches and the ledge isout to a depth of one-eighth inch. The anode block measures 1.576 inchesbetween the faces I! and I8 and has an over-all length between the endplates l9 and of 2.6 inches. The cathode diameter is three-sixteenthsinch. The straps are one-sixteenth inch wide and 0.02 inch thick and thetabs are 0.13 inch wide.

What is claimed is:

l. A cavity resonator comprising a block of conductive material having abore therein, said bore having an enlarged portion providing a ledge,and a plurality of conductive straps mounted upon said ledge, each saidstrap having a plurality of conductive tabs extending radially inwardtoward the center of said bore, each said tab having a portion extendingaxially along said bore, and positioned between said straps and theinner edge of said ledge.

2. A cavity resonator comprising a block having a bore therein having aportion of uniform diameter and an enlarged portion with a greaterdiameter, a plurality of shields in the enlarged portion and flush withthe inner surface of the bore portion of uniform diameter to simulate anextension of the uniform diameter into the enlarged portion, a strapwithin said enlarged portion in a position behind said shields betweensaid shields and the body of the block, and a plurality of metallic tabsconnecting said strap and said shields.

3. A cavity resonator comprising a block having a bore therein having aportion of uniform normal diameter, said bore also having an enlargedportion of a diameter greater than the said normal diameter, a strappositioned within the said enlarged portion of the bore and beyond thesaid normal diameter, and a plurality of tabs attached to said strap,each of said tabs comprising a radially extended portion conductivelyattached to said block and an axially extended portion substantiallyflush with the surface of the portion of the bore of normal diameter.

4. A cavity resonator comprising a block having a bore therein includinga portion of uniform diameter and having a plurality of axially extendedslots radiating outward from said bore, said bore also having a portionof enlarged diameter, a plurality of shields positioned in said enlargedportion between adjacent slots and flush with the surface of said boreportion of uniform diameter, a strap positioned behind said shields andwithin the limits of said portion of enlarged 6 diameter, and a tabconnecting said strap with one of said shields.

5. A resonator comprising a block of conductive material including aplurality of cavity resonators and having a perforation opening intosaid cavity resonators, said block having at least one face intersectingsaid cavity resonators and said perforation and having a ledgesurrounding said perfo-ratign and depressed with respect. to said face,a plurality of conductive straps mounted on said ledge and eachconnected to said block at a plurality of points on said ledge, and aplurality of conductive tabs attached to said straps extending towardsaid perforation and providing an array of shielding elements betweensaid straps and the said perforation.

6. A resonator comprising a block of condulctive material having acentral perforation and a plurality of slots and including a pluralityof cavity resonators each opening into said central perforation througha different one of said slots, said central perforation being enlargedat one end to provide a ledge, said ledge being divided into a pluralityof discrete portions by said slots, a plurality of conductive strapsmounted on said ledge and bridged between discrete portions thereof, anda plurality of conductive tabs attached to said straps extendinginwardly toward the axis of said central perforation and providing anarray of shielding elements between said straps and the central spacewithin said central perforation, whereby the said central space issubstantially shielded from the electromagnetic influence of the straps.

'7. A cavity resonator comprising a block of conductive material havinga central perforation and a plurality of peripheral perforationsangularly disposed around said central perforation and opening thereintothrough a plurality of individual slots, said central perforation havingan enlarged region providing a ledge, a plurality of conductive strapsmounted upon said ledge and contained Within the enlarged portion of thesaid central perforation, each said strap being conductively connectedto said block at a pair of points upon said ledge, said points beingseparated by one of said slots, and a plurality of conductive tabsattached to said straps and extending radially toward the axis of saidcentral perforation and having axially extending inner end portions,whereby the space within the central perforation is substantiallyshielded from the electromagnetic influence of the straps by means ofsaid inner end portions.

8. A cavity resonator comprising a block of conductive material having acentral perforation defining a reaction space therewithin and having aplurality of outer perforations around said central perforation andhaving a plurality of slots each opening into an outer perforation andinto the said central perforation, said block also having a ledgesurrounding said central perforation at one end of said block, aplurality of conductive straps mounted upon said ledge, each said strapbeing conductively connected to said block at a plurality of points, anytwo adjacent points of connection having a slot therebetween and aplurality of conductive tabs attached to said straps and extendingradially toward the axis of the block, and having axially extendingportions interposed between th straps and the central perforation,whereby the said reaction space is substantially shielded from theelectromagnetic influence of the straps.

9. A cavity resonator comprising a block having a. bore thereinincluding a portion of uniform diameter and having a plurality ofaxially extended slots radiating outward from said bore, said bore alsohaving a portion of enlarged diameter, a shield having an axiallyextended surface, said shield being mounted upon said block betweenadjacent slots and having its axially extended surface flush with thesurface of said bore porti'onof uniform diameter, a strap positionedbehind said shield and within the limits of said porton of enlargeddiameter, and a tab connecting said strap with said shield.

I VICTOR L. RONCI.

REFERENCES CITED The following references are of record in the file ofthis patent:

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